US2998000A

US2998000A - Device for performing an automatic grinding operation

Info

Publication number: US2998000A
Application number: US741662A
Authority: US
Inventors: Johansson Erik Lennar Waldemar
Original assignee: Svenska Kullagerfabriken AB
Current assignee: SKF AB
Priority date: 1957-06-24
Filing date: 1958-06-12
Publication date: 1961-08-29
Anticipated expiration: 1978-08-29
Also published as: FR1196786A

Description

Aug. 29, 1961 E. L. w. JOHANSSON 2,998,000

DEVICE FOR PERFORMING AN AUTOMATIC GRINDING OPERATION 2 Sheets-Sheet 1 Filed June 12, 1958 ZEdE mf/W Aug. 29, 19 1 E. L. w. JOHANSSON 2,993,000

DEVICE FOR PERFORMING AN AUTOMATIC GRINDING OPERATION Filed June 12, 1958 2 Sheets-Sheet 2 United States Patent i DEVICE FOR PERFORMING AN AUTOMATIC GRINDING OPERATION Erik i.ennart Waldemar Johansson, Goteborg, Sweden,

asslgnor to Aktiebolaget Svenska Kullagerfabriken,

Goteborg, Sweden, a corporation of Sweden Filed June 12, 1958, Ser. No. 741,662 Claims priority, application Sweden June 24, 1957 4 Claims. (Cl. 125-11) The present invention relates to an apparatus for grinding, and has particular application to grinding work pieces in series.

A primary object of the present invention is to provide an apparatus in which the rejection is reduced to a minimum, and the finish dimensions of the Work pieces are maintained in the center between the tolerance limits.

More specifically, the present invention provides modification of the dressing operation between rough grinding and finish grinding, to maintain the finish grinding operation within a predetermined time period.

When grinding Work pieces in series the grinding procedure is divided into three operations: rough grinding, dressing and finish grinding, which is also called spark out if there is no feed. In FIGS. 1, 2 and 3 the grinding sequence is shown in the form of diagrams, where the abscissa represents the time and the ordinate represents the position of the grinding wheel relative to the desired finished dimension. FIG. 1 shows an ideal grinding sequence. FIG. 2 shows a grinding sequence with too short spark out and FIG. 3 a sequence with too long spark out. FIG. 4 shows in outline an arrangement for using the procedure according to the invention. The same designations for corresponding points and details have been used in the figures.

G is a grinding wheel, where the extreme layer H, shown in finer sectioning, is the estimated wear and dressing allowance. The rough grinding is performed ac cording to curve A-B. From the point B the grinding Wheel is transferred from the work piece to a point C. It is dressed between C and D and returned to point B.

The spark out occurs from here to point F on the abscissa, when correct dimension is gauged. The spark out time is designated t. If, however, the feed is not eX- act-ly chosen, or if the grinding wheel wear during rough grinding is not in accord with the estimated wear, the grinding sequence may be diiferent. FIG. 2 shows a grinding sequence, where the grinding wheel feed has gone too far, or, alternatively, the wear on the grinding wheel has been less than the estimated wear. The spark out occurs too fast; the gauge does not react quickly enough, and consequently, the finished dimension is under the desired one, represented by the abscissa.

The spark out time 2 will be shorter than in the first case. FIG. 3, finally, shows a grinding sequence with a too small feed or too heavy grinding wheel wear. In this case, the gauge will react before the desired finished dimension has been reached. The spark out time is longer than in the ideal case, and consequently longer than ft-I) Generally speaking, the accuracy is a function of the duration of the fim'sh grinding. Thus, if this time can be held constant within a predetermined time period, the work pieces will all be accurately ground to the same size. Since the feed of the grinding wheel is step controlled, there is little or no possiblity of adjusting the position of the grinding wheel with sufficient accuracy. The cumulative efiect of small inaccuracies in the grinding of each work piece may result in a comparatively great deviation after a number of such operations. Another way is to adjust the dressing depth by regulating "2,998,009 Patented Aug. 29, 1961 the position of the dressing tool K, upon which the present patent application is based.

According to known designs, each work piece has been gauged after the operation, and when a work piece has dimensions outside of the tolerance limit, the position of the dressing tool has been adjusted. This method has several disadvantages. Primarily, the piece which is outside the tolerance limits must be rejected, and, secondly, the dimensions of the pieces will range evenly over the entire distance between tolerance limits. This means that the majority of the work pieces will not be in the center between the tolerance limits, which is desirable.

The present invention eliminates these diificulties and gives a product where the rejection percentage is practically nil. As stated above the accuracy is a function of the spark out time. Also, the spark out time is a function of the position of the dressing diamond and thus, the accuracy is a function of the position of the diamond. The present invention relates to a method and a device in automatic grinding machines where work pieces are produced in series and where the grinding wheel is dressed between a rough grinding and a finish grinding operation. It is characterized mainly thereby that the dressing depth is modified according to the duration of the finish grinding operation relative to a predetermined time period, i.e. when too short finish grinding, the dressing depth is increased and when too long finish grinding, the dressing depth is decreased.

One form of the invention is shown in outline in FIG. 4, which shows a device consisting of (1) a hydraulic or pneumatic timer and (2) a mechanism for adjusting the ressing tool position. In FIG. 4, 10 is a valve which opens and closes a supply conduit 11 for a pressure medium, e.g. air, and is another valve regulating the feed of this medium. The pressure medium operates a double-acting piston 12, on which a plunger 13 is mounted in the upper part. The plunger is limited by two chamfers 14 and 15 which have the same width and angle. The chamfer 14 continues in the piston rod 416 and the chamfer 15 continues in a circular end face '17. The piston 12 moves in a cylinder 18. To return the piston to the starting position there is a conduit 19 for the pressure medium.

The regulating device consists of a ratchet wheel 29 mounted on an axle 21 which operates the feed of a diamond for dressing the grinding wheel (not shown), when turning a suitable known angle. In the ratchet wheel Zil'mounted on the axle 21 thereis akeyway 22 which is slightly wider than the key 23 fitted in the axle. The key prevents the ratchet wheel from turning more than a small angle relative the axle. The function of this is described later. The ratchet wheel is operated by two pawl rods 24a and 24b mounted one on each side. On the top of these rods there are mounted pawls 25a and 25b respectively, which are kept in position against pins 26a and 261) by the springs 217a and 21717. The other ends of the rods consist of pistons 27a and 27b which are displaced upwardly by the pressure medium in cylinders 28a and 28b. The displacement is limited by adjusting screws 29a and 2% respectively. The pressure medium is supplied through pipes 210a and 21Gb regulated by valves 211a and 21112. The opening and closing of these valves is effected by one end of rods 212a and 21219, which in the other ends have rollers 213a and 2131) respectively, suitably ball bearings. The rollers can turn in the plane of the rods 212a and 212b respectively and the plunger 13. The valves are biased toward close position by means of springs 214a and 214b. The pistons 27a and 27b are biased toward the bottom position by springs 216a and 2161).

The device works as follows: When the finish grinding 3 operation is started, the valve 10 opens and the compressed air forces the piston 12 to move slowly upwards until the finish grinding ends and the valve closes. During this movement the piston in turn operates the rollers 213a and 213b, and valves 211a and 211b open. Depending on the duration of the finish grinding operation the piston 13 stops in one of three different positions: (a) opposite the roller 213a which has been moved in and opened the valve 21 1a; (b) between the rollers 213a and 2131), where neither the valve 211a nor 211k is open, and, finally, (c) opposite the roller 213b, which has been moved in and opened the valve 211b.

In the case (a) the spark out time has been too short, and the grinding wheel has to be dressed deeper; in the case (b) the spark out time has been correct and within a predetermined time period, and no adjustment of the diamond position is necessary; and in the last case, the spark out time has been too long, and the dressing has been too deep. When the grinding operation is finished, the air supply to the pipes 210a and 21% is opened. If either one of the valves 211a and 21-1b is opened, the associated piston 27a or 27b will move upwards and operate the ratchet wheel regulating the diamond position. Lost motion means is provided by the play between the ratchet wheel 20 and the key 23 which has been chosen so that the axle 21 will not be driven until there have been three more impulses in one direction than in the other. Thus, an occasional deviation of the finish will not change the position of the diamond. If the plunger 13 has stopped three times opposite the roller 213a, the axle 21 will turn an angle corresponding to one tooth of the ratchet wheel, and the diamond will feed a few microns. If the next stop position should be the same, the diamond will be fed further until the position of the plunger attains the desired position between the rollers 213a and 21317. If the limits are kept close the dimensional limits of the finished product will be near the centre of the tolerance, and very few if any will fall outside the tolerance.

The arrangement as described might be altered, e.g. the hydraulic time relay might be substituted by an electrical one.

I claim:

1. In a grinding machine, a grinding wheel operable to rough-grind in one operation and finish grind in a succeeding operation, a dressing tool operated to dress said wheel to a given depth between said operations, a timer operated concurrently with said finish-grinding operation, said timer having an operator in one position prior to a predetermined time period, in a second position during said predetermined time period, and in a third position r 4 after said predetermined time period, and control means receiving impulses from said operator at the termination of said finish grinding operation operable to cause relative movement of the dressing tool and grinding wheel in a direction toward one another when said operator is in said first position, and operable to cause relative movement of the dressing tool and grinding wheel in a direction away from one another when said operator is in said third position, said control means having lostmotion means for delaying said relative movement until the impulses tending to cause said relative movement in one direction exceed the impulses tending to cause said relative movement in the opposite direction by a predetermined number.

2. A device according to claim 1, wherein said timer comprises a cylinder, a piston displaceable in said cylinder and mounting said operator for saidcontrol means, and fluid pressure supply means connected to said cylirr-. der during said finish grinding operation to displace said piston and position said operator in accordance with the duration of said finish grinding operation.

3. A device according to claim 1, wherein said control means comprises a ratchet wheel connected to said dressing tool, a first pawl rod displaceable to effect said relative movement of the dressing tool and wheel toward one another to advance said dressing tool, a second pawl rod displaceable to effect said relative movement of the dressing tool and wheel away from one another to retract said dressing tool, means to displace said first pawl means when said operator is in its first position,'and means to displace said secondpawl means when said operator is in its third position.

4. A device according to claim 3 including a drive axle connecting said ratchet wheel to said'dressing tool, and wherein said lost-motion means is disposed between said ratchet wheel and said axle, said lost motion means requiring a given number of displacements of one pawl rod in excess of displacements of the other pawl rod to effect displacement of said axle and said dressing tool.

References Cited in the file of this patent UNITED STATES PATENTS 2,459,641 Hallead Jan. 18, 1949 2,720,063 'Hill Oct. 11, 1955 2,829,530 Holden Apr. 8, 1958 2,850,847 Townsend Sept. 9, 1958 2,881,568 Hahn et a1. Apr. 14, 1959 2,932,130 Blood et a1. Apr. 12, 1960 FOREIGN PATENTS 7 703,224 Great Britain Jan. 27, 1954